Glycogen

Definition

A highly branched polysaccharide of glucose that serves as the principal short-term energy reserve in animals, fungi, and bacteria. In arthropods, glycogen is synthesized in the fat body and muscle tissue, then mobilized via trehalose synthesis to fuel flight, molting, reproduction, and diapause. Unlike the more stable lipid reserves used for long-term fasting, glycogen provides rapid, anaerobically accessible glucose units for sudden bursts of activity.

Etymology

From Greek 'glykys' (sweet) + '-gen' (producing)

Example

Honey bees accumulate glycogen in flight muscles before foraging flights; during winter cluster thermogenesis, they metabolize these stores to generate heat through non-shivering thermogenesis.

Synonyms

• animal starch
• liver starch

Related Terms

• Trehalose
• Fat body
• Diapause
• glycolysis
• gluconeogenesis
• Hemolymph
• lipid storage

Usage Notes

Distinguished from starch (the plant storage equivalent) by its greater branching density (α-1,6 linkages every 8–12 glucose units versus every 24–30 in amylopectin). In entomology, glycogen levels are commonly measured as a physiological index of nutritional status, stress, or readiness for dormancy. Not to be confused with glycogen-like inclusion bodies in bacteria (e.g., species epithets such as *glycogenes*).